import java.util.LinkedList;
import java.util.Queue;

public class Solution2 {
    public int numIslands(char[][] grid) {
        int m = grid.length;
        int n = grid[0].length;
        int[] dx = {0, 0, 1, -1};
        int[] dy = {1, -1, 0, 0};
        boolean[][] check = new boolean[m][n];
        int ret = 0;

        Queue<int[]> q = new LinkedList<>();
        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                if(grid[i][j] == '1' && check[i][j] == false) {
                    q.add(new int[]{i, j});
                    while(!q.isEmpty()) {
                        int[] t = q.poll();
                        int a = t[0];
                        int b = t[1];
                        for(int k = 0; k < 4; k++) {
                            int x = a + dx[k];
                            int y = b + dy[k];
                            if(x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1' && check[x][y] == false) {
                                q.add(new int[]{x,y});
                                check[x][y] = true;
                            }
                        }
                    }
                    ret++;
                }
            }
        }
        return ret;
    }

    int m;
    int n;
    int[] dx = {0, 0, 1, -1};
    int[] dy = {1, -1, 0, 0};
    boolean[][] check;
    public int numIslands1(char[][] grid) {
        m = grid.length;
        n = grid[0].length;
        check = new boolean[m][n];
        int ret = 0;

        Queue<int[]> q = new LinkedList<>();
        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                if(grid[i][j] == '1' && check[i][j] == false) {
                    q.add(new int[]{i, j});
                    bfs(grid, q);
                    ret++;
                }
            }
        }
        return ret;
    }

    public void bfs(char[][] grid, Queue<int[]> q) {
        while(!q.isEmpty()) {
            int[] t = q.poll();
            int a = t[0];
            int b = t[1];
            for(int k = 0; k < 4; k++) {
                int x = a + dx[k];
                int y = b + dy[k];
                if(x >= 0 && x < m && y >= 0 && y < n && grid[x][y] == '1' && check[x][y] == false) {
                    q.add(new int[]{x,y});
                    check[x][y] = true;
                }
            }
        }
    }
}
